Elizabeth Taylor Remembered at Private Memorial for Friends, Family

Close friends and family of the late Elizabeth Taylor gathered Sunday afternoon to remember the beloved Hollywood legend during a private memorial on the Warner Brothers lot in Burbank, PEOPLE has learned.

With Taylor's good friend Colin Farrell hosting the 75-minute celebration in the lot's Steven J. Ross Theater, the tribute was attended by Taylor's children Michael and Christopher Wilding, Liza Tivey and Maria Burton, as well as close friends Michael Caine, stepdaughter Kate Burton and Sir Elton John, who sang a stirring rendition of "Blue Eyes" to close the program.

"To say that the world got smaller, emptier, darker and lonelier when we lost Elizabeth is an understatement," Sir Elton John told the 400 guests during his heartfelt remarks. "She was a true rock, a pioneer, a pathfinder, a trailblazer and a star who will always burn bright and always had time to laugh at herself."

Her Beauty, Her Humor

Throughout the program, guests spoke of Taylor's humor, beauty and generosity, and shared memories from her rich and colorful life. Taylor died of congestive heart failure on March 23. She was 79.

One especially touching moment came when grandson Rhys Tivey stood up and played a trumpet rendition of "Amazing Grace," a song his grandmother loved. "People were mesmerized how her talent and grace lived on in Rhys," says a guest.

There were also tributes to the three-time Oscar-winner's post-Hollywood career, both as a businesswoman with her fragrance White Diamonds, and her tenacious advocacy on behalf of people living with HIV/AIDS. AIDS activists in the audience were visibly moved as clips of Taylor lobbying in Washington, D.C., in the early '80s played on the screen.

"Many of us remember all too well, those early days of the AIDS epidemic in the early to mid-1980s," said Sir Elton. "It brought out the worst – hysteria, bigotry, callous indifference. But it also allowed an angel and warrior, like Elizabeth, to rise up and show us how to respond instead with compassion, reason, and humanity."

Taylor's son Michael, from her 1952 marriage to British actor Michael Wilding, told PEOPLE: "My mother was an extraordinary woman whose life touched so many, most of whom we will never know.

"Our whole family is extremely proud of her accomplishments, and know what a unique and special experience it was to have her in our lives. Today, it was especially meaningful for us to be with so many good friends to celebrate her spirit, which will be with us forever."